Vehicle dynamics control systems, understood to include all the devices that intervene in the driving operation via operation of brakes or drive such as ABS (anti-lock brake system), TCS (traction control system), ESP (electronic stability program) or MSR (engine drag torque control), help to stabilize motor vehicles in borderline situations in particular. To further improve controllability, vehicles are increasingly being equipped with active normal force adjustment systems, which are also referred to as spring-damper systems with which the normal force (wheel contact force) of a wheel is adjustable as a function of the driving situation. The function of the active normal force adjustment system such as CDC (continuous damper control) or ARC (active roll control) is to reduce vertical acceleration of the vehicle body and/or to compensate for the rolling motion of the vehicle when turning a corner and in horizontal leveling of the vehicle.
A two-channel ARC system has, for example, actuators on the front and rear axles which may be under tension independently of one another with respect to the passive state. However, when there is different tension on the front and rear axles, the normal forces (contact forces) on the wheels change. Because the lateral guidance force of the wheels increases only degressively as the normal force increases, the self-steering effect of the vehicle thus also changes. Depending on the setting of the normal force adjustment system, the vehicle thus exhibits either a more oversteering behavior or a more understeering behavior in comparison with the passive state. This has negative effects in particular on a vehicle dynamics control which is performed in parallel.
Vehicle dynamics control systems are usually based on a fixed self-steering effect. A self-steering effect altered by the normal force adjustment system may therefore result in faulty braking operations when the actual performance of the vehicle differs too much from the calculated setpoint performance.
In addition, the traction control implemented as part of the dynamics control is impaired. In order to adapt the brake slip controller to the particular driving situation, the normal forces acting on the wheels are usually estimated. Operation of the normal force adjustment system results in a deviation between the estimated and actual normal forces and may thus result in a malfunction of the traction control system.